Bronze, discovery

FIGURE 1 Copper is easily extracted from its ores and was one of the first metals worked. The Bronze Age followed the discovery that adding some tin to copper made the metal harder and stronger. These four bronze swords date from 1250 to 850 hce, the Late Bronze Age, and are from a collection in the Naturhistorisches Museum, Vienna, Austria. From bottom to top, they are a short sword, an antenna-type sword, a tongue-shaped sword, and a Liptau-type sword. 

These properties, coupled with its relatively low cost, make copper one of the most useful metals in modem society. About half of all copper produced is for electrical wiring, and the metal is also widely used for plumbing pipes. Copper is used to make several important alloys, the most important of which are bronze and brass. Both alloys contain copper mixed with lesser amounts of tin and zinc in various proportions. In bronze, the amount of tin exceeds that of zinc, whereas the opposite is tme for brass. The discovery of bronze sometime around 3000 bc launched the advance of civilization known today as the Bronze Age. Because bronze is harder and stronger than other metals known in antiquity, it became a mainstay of the civilizations of India and the Mediterranean, used for tools, cookware, weapons, coins, and objects of art. Today the principal use of bronze is for bearings, fittings, and machine parts. 

Prior to the Civil War, engineers were pretty well limited to working with only a few materials, such as iron, copper, tin, zinc, brass and bronze and, of course, wood. Steel became more readily available shortly after the Civil War through the wider use of the recently discovered Bessemer and open-hearth processes and the subsequent discovery of alloy steels. And around the turn of the century, aluminum was becoming available in commercial quantities. 

If a small piece uf an alkali metal is dropped into a Dewar task containing liquefied ammonia, the solution immediately assumes an intense deep blue color. If more alkali metal is dissolved in the ammonia, eventually a point is reached where. 1 bronze-colored phase separates and floats on the blue solution.- Further addition of alkali metal results in the gradual conversion of blue solution to bronze solution until the former disappears. Evaporation of the ammonia from the bronze solution allows one to recover the alkali metal unchanged.) This unusual behavior has fascinated chemists since its discovery in 1864. Complete agreement on the theoretical interpretation of experimental observations made on these solutions has not been achieved. 

The first significant breakthrough in metallurgy occurred some time after the fourth millennium b.c.e. Metallurgy is the study of metals and the process by which they are extracted from the Earth and converted to useful objects, such as alloys. This event was the discovery of methods for the production of bronze, the first alloy. An alloy is a mixture of two or more elements (at least one of which is a metal) with properties different from those of the elements themselves. Bronze is made from copper and tin in a ratio of at least 9 parts copper to 1 part tin. The temperature required to convert the two elements into the alloy is relatively low (slightly more than the melting point of copper, 1,083°C) and could he attained in ovens available at the time. 

The approval of Taxol for marketing in December 1992 was the culmination of 35 years of work. During this period of time the National Cancer Institute (NCI) and the U.S. Department of Agriculture (USDA) collaborated to collect, identify, and screen U.S. native plant material for antitumor activity. The year 1992 also marked, coincidentally, the discovery of the Ice Man in the Italian Alps. This Bronze Age man, who died 5300 years ago, was found in possession of a pure copper axe set in a yew wood handle and an unfinished 6-foot yew bow. Obviously, the yew tree has played a number of important roles for humans throughout history. 

As you know from Chapter 4, solid solutions of metals are called alloys. Adding even small quantities of another element to a metal changes the properties of the metal. Technological advances throughout history have been linked closely to the discovery of new alloys. For example, bronze is an alloy of copper and tin. Bronze contains only about 10% tin, but it is much stronger than copper and more resistant to corrosion. Also, bronze can be melted in an ordinary fire so that castings can be made, as shown in Figure 8.3. 

The ages of Stone, Bronze, and Iron are well-known periods in the history of civilization. Not so well known is the Chalcolithic Age (4300-3200 b.c.). The name comes from the Greek for copper and stone, and the Chalcolithic Age is the period between the Stone and Bronze Ages when implements of both stone and copper were used side by side. This age might have remained obscure to all but a few specialists except for one remarkable discovery—the Iceman. 

Alloys are materials composed primarily of one metal, called the parent metal, doctored with smaller amounts of other metals or nonmetals. When tin or arsenic is added to copper, the metal becomes harder, stronger, and easier to cast. This metallic mixture is known as bronze, and its discovery ushered in a whole new suite of tools, weapons, armor, and decorative objects. So dramatic was the change from the copper and stone implements that preceded it, that bronze became the defining feature of the period, now known as the Bronze Age. Alloys such as bronze have played and continue to play a huge role in building the modern world. 

The original interest in these excavated samples stemmed from the important role of bronze and the historical implications of the extensive tin trade routes in the Middle Bronze Age (2200-1600 B.C.). As bronze metallurgy developed from the earlier use of copper and arsenical copper, tin sources became vital (14). By the Middle Bronze Age, the limited distribution of tin deposits throughout the world and the ample supply of copper were well-known, and extensive tin trade routes had been established to supply the metallurgical centers of the world with this then-considered precious metal (15-16). The Ugaritic tablets from Ras Shamra, however, indicate a severe drop in the value of tin around the Late Bronze Age (1400-1200 B.C.). It has been postulated (17) that this drop was related to the discovery of more accessible sources of tin. 

Metal alloys were first used in the Bronze Age (1,400 B.C.-O B.C.), where serendipity led to the discovery that doping copper with other compounds drastically altered the physical properties of the material. Artifacts from the Middle East dating back to 3,000 B.C. are found to consist of arsenic-doped copper, due to the wide availability of lautite and domeykite ores, which are rich in both arsenic and copper. However, due to arsenic-related casualties, these alloys were quickly replaced with tin-copper alloys (bronze) that were widely used due to a lower melting point, higher hardness, and lower brittleness relative to their arsenic forerunner. 

Of all the 115 elements listed in the Periodic Table, 70% exhibit metallic character. Since the discovery of copper and bronze by early civilizations, the study of metals i.e., metallurgy) contributed to most of the early investigations related to materials science. Whereas iron-based alloys have long been exploited for a variety of applications, there is a constant search for new metallic compositions that have increasing structural durability, but also possess sufficiently less density. The recent exploitation of titanium-based alloys results from this effort, and has resulted in very useful materials that are used for applications ranging from aircraft bodies to golf clubs. Indeed, there are many yet undiscovered metallic compositions that will undoubtedly prove invaluable for future applications. 

The atomic radii of Cu, Sn(1.45 A), and Zn(1.42A) are also nearly identical, allowing for a full gamut of Cu/Sn and Cu/Zn alloy concentrations to be produced, known as bronze and brass, respectively. Although the use of bronze dates back to at least 3,000 B.C., there are also early examples of brass artifacts that date back to ca. 2,200 B.C. in India. Most likely, the discovery of bronze resulted from the inquisitive mixing of available metals at the time, only to discover that Au/Sn alloys possessed a greater strength than iron steels were not developed until thousands of years later. Since zinc metal was not available until the mid-18th century, and tin was readily obtained, the widespread production of bronzes occurred at the expense of brasses. In the absence of pure zinc, early formulations of Cu/Zn alloys were most likely... 

Bronze became popular among ancient peoples because it was harder and tougher than copper. Before the discovery of bronze, many metal items were made out of copper. But copper is soft and bends easily. Bronze is a much better replacement for copper in tools, eating utensils, and weapons. Bronze marked a significant advance in human civilization. This strong alloy improved transportation methods, food preparation, and quality of life during a period now known as the Bronze Age (3500—1000 bce). 

It is important to note the existence of ancient Northern European rock drawings that depict various mushroom themes, along with the discovery of bronze-age vessels decorated with... 

Tin has been known as a metal since time immemorial, and the discovery, in abont 3500 bc, that it formed a strong, hard alloy with copper, started the Bronze Age, which lasted nntil abont 1200 bc. 

A parallel glass making tradition developed in China, again following the discovery of the pyrotechnology associated with bronze production. In China, however, lead oxide was used instead of alkali elements as the flux and barium, instead of calcium and magnesium, was used to stabilize glass. 

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